This invention is generally directed to processes for modifying the electrical properties of certain substances, and more specifically, the present invention is directed to a process for the surface treatment of selenium and selenium alloys, for the primary purpose of improving the electron transporting properties of these substances. Thus in accordance with the process of the present invention, certain selected reducing agents, such as hydrozine, are caused to be homogeneously permanently absorbed, or chemisorbed on the surface of selenium, or selenium alloys for the purpose of extending the electron transporting range capabilities of these materials. Accordingly thus subsequent to treatment in accordance with the process of the present invention the electrical behavior of selenium, or selenium alloys is desirably modified.
The selection of selenium or selenium containing substances as xerographic imaging members is well known in the art. These members are generally subjected to a uniform electrostatic charge for the purpose of sensitizing the surface of the photoconductive layer, followed by exposure of an image to activating electromagnetic radiation, such as light, which selectively dissipates the charge in the illuminated areas, of the photoconductive insulating member, and wherein a latent electrostatic image is formed in the non-illuminated areas. The resulting image may then be developed and rendered visible by depositing thereon toner particles. In addition to single layer selenium imaging members, recently, there has been disclosed layered organic and inorganic photoresponsive devices containing amorphous selenium, trigonal selenium, amorphous selenium alloys, halogen doped selenium, halogen doped selenium alloys, phthalocyanines, and the like. One such photoresponsive member is comprised of a substrate, a photogenerating layer containing trigonal selenium, or vanadyl phthalocyanine dispersed in a resinous binder, and a transport layer containing a diamine dispersed in a resinous binder, reference, U.S. Pat. No. 4,265,990.
With regard to single layer photoresponsive devices containing amorphous selenium or amorphous selenium alloys, during the latent image formation step, light is absorbed in a thin region in close proximity to the positively charged top surface. The resulting photoinjected holes, or positive charges, which are then injected into the selenium substance for example, are primarily responsible for causing discharge. In multi-layered photoresponsive devices containing inorganic photogenerators and organic transport layers, light is absorbed in the photogenerator layer, and the resulting photogenerated holes are injected and move through a transport layer. Therefore, amorphous selenium, or its alloys, which are used in such photoresponsive devices are considered to have extended hole range capabilities.
With regard to photoresponsive devices consisting of selenium or selenium alloys, where the surface is negatively charged, the resulting photogenerated electrons which are injected into the selenium substance for example are primarily responsible for causing discharge. Selenium or selenium alloys, selected for use in such devices are thus required to possess extended electron range capabilities. Therefore, for electrophotography selenium or selenium alloys with either extended electron and/or extended hole range are desired.
Presently, processes for preparing selenium result in photoconductive materials wherein the electrical properties of selenium cannot be predicted, and/or modified. Thus, for example, there is disclosed in U.S. Pat. Nos. 4,007,255 and 4,009,249 the preparation of stable, red amorphous selenium containing thallium, and the preparation of red amorphous selenium. In U.S. Pat. No. 4,007,255 there is disclosed a process for preparing an amorphous red selenium material containing thallium, which involves precipitating selenious acid containing from about 10 parts per million to about 10,000 parts per million of thallium dioxide, with hydrazine, from a solution thereof in methanol or ethanol, containing not more than about 50 percent by weight of water, at a temperature between about -20.degree. C. and the freezing point of the solution and maintaining the resulting precipitate at a temperature of about -15.degree. C. to about -3.degree. C. until the solution turns to a red color. The U.S. Pat. No. 4,009,249 contains a similar disclosure with the exception that thallium is not contained in the material being treated.
Moreover there is disclosed in copending application Ser. No. 404,259 a process for obtaining selenium and selenium alloys in high purity by forming the esters of the desired elements, followed by separating the esters, and subjecting the esters subsequent to purification by crystallization or distillation to a reduction reaction with for example hydrazine, or sulfur dioxide.
There continues to be a need for improved processes for preparing photoconductive substances such as selenium, and selenium alloys with extended electron range capabilities. Additionally, there continues to be a need for an improved simple economical process wherein selenium of modified electrical properties can be prepared. Additionally, there continues to be a need for improved processes wherein the electrical properties of commercially available selenium, or commercially available selenium alloys can be desirably modified.